It's a formal phrase, one that I believe originates in the world of politics. A person who can speak to something is one who has some authority or expertise on the matter, or will give evidence or commentary on it. Example: An expert witness will speak to the merits of a pending piece of legislation. It's a turn of phrase that makes me just a tiny bit nostalgic for my days as a legislative aide! Walk to Rivendell: There and Back Again Challenge - getting thirteen rowdy Dwarves, one grumpy Wizard, and a beleaguered Hobbit from Bag End to the Lonely Mountain by December 2012; and that same much enriched Hobbit back to Bag End by December 2013